Method of preparing pipe systems for chemical cleaning



United States Patent Office 3,036,559 Patented May 29, 1962 3,036,559 METHOD OF PREPARING PIPE SYSTEMS FOR CHEMICAL CLEANING Siegfried Kohler, Dusseldorf, Germany, assignor to Borg Holding A.G., a corporation of Switzerland No Drawing. Filed Nov. 18, 1958, Ser. No. 774,613 Claims priority, application Germany Nov. 23, 1957 3 Claims. (Cl. 122379) This invention relates to methods of preparing pipe systems for chemical cleaning and more particularly to methods for removing air pockets from elevated internal regions of the system.

The treatment of the internal surfaces of pipe systems exposed to Water in steam generators by chemical methods is used for the regular cleaning of installations already in operation to remove incrustations such as boiler scale. Frequently such installations are chemically pretreated before being put into operation in order to make the internal surfaces of the evaporator part and the superheater metallically bright and to remove rolling scale and foreign bodies accumulated during manufacture, for example, gravel, sand, etc. In either case it is of great importance that all pipe sections to be treated chemically are uniformly filled with cleaning fluid and then are traversed thereby. In cases Where the cleaning fluid contains acid, which after treatment would lead to corrosion and possibly to the destruction of the pipes if they were left in the installation, it is essential that the pipe sections be thoroughly flushed with rinsing agents.

Hitherto a number of dilficulties were met in the case of water or superheater pipes which are supported in vertically extending positions with regard to providing a successful chemical cleaning thereof.

Generally an installation to be treated is filled with Water permeated with air bubbles and air pockets. The water, in the case of treatment before operating the installation, originates from the hydraulic proof test. In the case of treatment after operating the boiler, both the boiler and the superheater are partly filled with feed or condensation Water respectively. Thus, if there are air pockets contained in the individual vertically extending runs of continuous pipe sections, it is necessary when moving the air-water column in the alternately ascending and descending runs of the pipe passes, to overcome not only the dynamic flow resistance but also a static back pressure. The latter corresponds to the Weight difiierence of the water columns in the series of vertically extending runs of the pipe. In practice the static back pressure may reach the value of several meters of water column and thus exceed by a multiple the flow resistance of the flow velocities concerned. This makes the scavenging difi'icult and demands a substantially increased expenditure of energy by the pumping'unit to overcome the static back pressure.

Of much greater importance, however, is a phenomenon which occurs in a large number of parallel mounted pipe passes having sections which extend in inclined or vertical directions. The random distribution of the air pockets in individual parallel mounted pipe runs causes the static back pressure in the different parallel mounted pipe coils to vary within wide limits. As the flow of liquid chooses the path of least resistance, only the pipe runs having a low static back pressure are scavenged. From these pipe runs the air pockets are removed, whereby the static pres sure therein is removed. The overall resistance of the pipe runs having a lower starting resistance is thus further reduced. On the other hand the resistance in the remaining pipe runs remains unchanged, and these are entirely excluded from the throughput of the chemical treatment.

The presence of such inactive pipe runs in the through- 2 flow during the chemical treatment can in practice only be eliminated by increasing the flow velocity. The dynamic flow resistance must therefore exceed the static back pressure. This cannot be attained with an expenditure of pumping elfort which is still economical.

The conditions described above have led to a general opinion in expert circles that the chemical treatment of elevated or vertically supported runs of water pipe boilers and superheaters, although desirable, cannot be carried out in practice.

It is a primary object of the invention to provide a method for preparing systems of the aforementioned types for chemical treatment, in which method air pockets are eliminated from elevated internal regions of the systems.

According to the present invention the pipe system to be chemically cleaned (boiler or superheater) is first connected to a boiler which is in operation which serves as a source of saturated steam and blown out with a sufficient supply of steam from the operating boiler. This step in the operation may be brought about or assisted by heating the pipe system to be cleaned. In this way water and air pockets within the system are completely removed. When treating superheaters the boiler associated therewith is used conveniently for the steam supply. In the latter case, the boiler is put under pressure on completion of the blowing out operation, after the discharge openings of the superheater are closed. The superheater in the case of normal circulating boilers thus cools 01f substantially more quickly than the evaporator part, so that the steam content of the superheater is condensed under pressure. The supply of steam obtained by means of the excess pressure of the boiler causes a continual complete and entirely air-free water filling of the superheater.

The superheater may also be caused or assisted to cool ofi? by putting into operation the blown or by other suitable cooling devices and agents. The forming of a vacuum in the drum is prevented by an additional feed or feed water. In the case of positive passage boilers the formation of a vacuum, with an extinguished fire and substantially throttled discharge conduit, is reduced by continued operation of the feed pump. The method when treating water pipe boilers is more simplified by the fact that in this case the furnace of the steam supplying boiler regardless of the cooling of the pipes to be cleaned and with the blower in operation, need not be shut down.

It will be obvious to the skilled in the art that various changes and modifications may be made therein without departing from the invention and, therefore, it is aimed to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What is claimed is:

*l. The method of preparing the pipe system of a boiler installation having a forced draft heating system for subsequent chemical cleaning comprising the steps of passing saturated steam under pressure through the pipe system being prepared While the pipe system is heated by the operation of the heating system, and stopping operation of the heating system associated with the pipe system being prepared to permit the pipe system to cool While saturated steam under pressure is continuously supplied thereto until the pipe system is filled with condensate.

2. The method of preparing the pipe system of a boiler installation having a forced draft heating system having a draft inducing blower for subsequent chemical cleaning comprising the steps of operating said heating system to heat the pipe system, passing saturated steam under pressure from an external source through the pipe system while said heating system is in operation, and subsequently stopping operation of said heating system while continuing to supply saturated steam under pressure from the external source to said pipe system While said pipe systern cools as a result of the stopping of operation of said heating system until the pipe system is filled with condensate.

3. The method as defined in claim 2 including the step of discontinuing the supply of saturated steam under pressure to said pipe system, and subsequently actively cooling said pipe system by operating the blower of said heating system to induce a forced draft in said installation While maintaining the heating units of said system inactive.

References Cited in the file of this patent UNITED STATES PATENTS Opper Aug. 29, 1882 Thomas Dec. 15, 1914 Murphy Nov. 15, 1938 Dixon July 14, 1942 Duvall Mar. 9, 1954 FOREIGN PATENTS Great Britain Aug. 10, 1960 

